The present invention relates generally to methods and apparatuses for sensing and determining the level of contaminants in a fluid, and, more particularly, to improved fluid contaminant measuring apparatuses and methods that closely simulate the physical conditions that such fluid will likely encounter in use.
This invention provides a fluid contamination measuring apparatus that is closely related to the equipment described in British Patent Application No. 00 17 987.9, which is owned by the assignee of the present application. That system utilizes a contaminant sensing orifice that simulates the annular clearance between a closely-fitted valve spool land and its associated sleeve. The sensing orifice is itself defined between a valve spool land and a bore wall. The valve spool may be selectively moved in an axial direction to align the spool land with a sleeve recess of an enlarged diameter for flushing accumulated contaminant particles from the test orifice prior to the beginning of a test cycle.
The testing technique of exposing an initially-clean test orifice to flow of a contaminated fluid and observing the effect of progressive attenuation of flow as contaminant particles accumulate in the test orifice has apparently been known for many years. Known measurement techniques appear to fall into two broad categories.
In the first, the flow is directly measured, usually by means of a piston. This piston can be used to drive fluid through the test orifice, or to collect fluid passing through the test orifice. In either case, the piston displacement vs. time data enables flow through the orifice to be calculated. Examples of this type are shown in U.S. Pat. Nos. 4,663,966 and 4,495,799 (see FIG. 3 thereof).
In the second category, the test orifice is connected in series with a source of pressurized fluid and a reference orifice having an impedance to flow similar to that of the test orifice. As the test orifice becomes progressively occluded by contaminants, the flow and the pressure drops across the series-connected restrictions will change, providing a basis for calibrating and determining the extent of contamination. An example of this type is shown in U.S. Pat. No. 4,495,799 (see FIGS. 1 and 2 thereof). The ""799 patent discloses an arrangement for passing pressurized fluid through an upstream reference orifice, described as a sharp-edged restriction having an opening much larger that the clearance of the annular test orifice, and then through the test orifice itself. A pressure sensing mechanism is then used to measure the pressure drop across the test orifice.
A potential difficulty with this sort of apparatus is that the flow is laminar, and hence sensitive to changes in fluid viscosity and temperature. Pressure drops across the reference and test orifices can be expected to vary in several ways, even in the absence of a contaminant, and can introduce significant errors into the measurement. An attempt to deal with this shortcoming is shown in U.S. Pat. No. 4,685,066, in which a test filter (i.e., a porous disk, rather than an annular orifice) is arranged in series with a similar filter as a reference restriction. The upstream test filter will collect and accumulate particulate contamination, and the downstream filter will pass any particles that have passed through the test filter. Both elements will tend to have the same temperature sensitivity. Hence, that factor can be eliminated as a factor in the testing protocol.
With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, the present invention broadly provides improved methods and apparatuses for determining the extent of contaminants in a fluid.
In one aspect, apparatus (20) for testing the extent of contaminants in a fluid during a test period, comprises: a source of pressurized fluid (Ps) to be tested; a fluid sump (R); a first flow restriction (R1) adapted to be supplied with fluid flow from the source, the first flow restriction being configured as an annular clearance between a first land (24) and a first bore (22) and being sized and arranged so as to be progressively occluded by contaminants in the fluid flow during the test period; a second flow restriction (R2) arranged between the first flow restriction and the sump, the second flow restriction being configured as an annular clearance between a second land (25) and a second bore (22), the second flow restriction being substantially the same dimensionally as the first flow restriction so that the second flow restriction will not be occluded by contaminants passing through the first flow restriction and the pressure drops across each of the flow restrictions will be substantially equal at the beginning of a test period.
In this form, as the first flow restriction (R1) becomes progressively occluded by contaminants in the fluid flow during the test period, the pressure drop across the first flow restriction will increase and the pressure drop across the second flow restriction (R2) will decrease, such that the extent of contamination in the fluid will be indicated as a function of a change in pressure or as a change in the ratio of the pressure drops.
The apparatus may include a pressure sensor (45) operatively arrange to measure the fluid pressure between the first and second flow restrictions, such that the extent of contamination in the fluid will be indicated as a function of a change in such sensed pressure.
The flow restriction lands (24, 25) may be provided on a first valve spool (21) movably mounted in a first bore and adapted to be moved in one axial direction relative to the first bore to allow the flow restrictions to be flushed of contaminants prior to the commencement of a test period.
In another aspect, the second land (61) may be provided on a second valve spool movably mounted in a second bore (63). This second flow restriction (R2) may have a substantially-constant radial clearance and a variable axial length (L2). The second flow restriction may have an impedance to flow that is a function of the extent to which the second land overlaps the second bore. The apparatus may further include a sensor (72) for sensing the length of the second flow restriction.
The length of overlap (L2) between the second land and the second bore may be arranged to be selectively increased during the test period so as to cause the pressure drop across the second flow restriction to be maintained substantially equal to the pressure across the first flow restriction as the first flow restriction becomes progressively occluded, such that the extent of contamination in the fluid will be indicated as a function of the length of the overlap.
The second spool may be similarly adapted to be moved in one axial direction relative to the second bore to allow the second flow restriction to be flushed of contaminants prior to the commencement of a test period. The apparatus may include a regulator (56) operatively arranged to change the impedance of the second flow restriction so that the fluid pressure between the flow restrictions will remain substantially constant, such that the extent of contamination in the fluid will be indicated as a function of the change of impedance of the second flow restriction.
In another aspect, the invention provides a method of testing the extent of contaminants in a fluid during a test period, comprising the steps of: providing a source of pressurized fluid to be tested; providing a fluid sump; providing a first flow restriction configured as an annular clearance between a first land and a first bore; causing fluid from the source to flow through the first flow restriction; progressively occluding the first flow restriction with contaminants in the fluid flowing therethrough; providing a second flow restriction between the first flow restriction and the sump, the second flow restriction being configured as an annular clearance between a second land and a second bore and being sized so as to not be occluded by contaminants passing through the first flow restriction; and monitoring the fluid pressure between the first and second flow restrictions; thereby to indicated the extent of contaminants in the source fluid as a function of the change in such monitored pressure during the test period.
According to this method, accumulated contaminants may be removed or flushed from the first flow restriction prior to the beginning of the test period.
In still another aspect, the invention provides a method of testing the extent of contaminants in a fluid during a test period, comprising the steps of: providing a source of pressurized fluid to be tested; providing a fluid sump; providing a first flow restriction configured as an annular clearance between a first land and a first bore; causing fluid from the source to flow through the first flow restriction; progressively occluding the first flow restriction with contaminants in the fluid flowing therethrough; providing a second flow restriction between the first flow restriction and the sump, the second flow restriction being configured as an annular clearance between a second land and a second bore; and varying the impedance of the second flow restriction as a function of the fluid pressure between the first and second flow restrictions; thereby to indicate the extent of contaminants in the source fluid as a function of the change in impedance of the second flow restriction during the test period.
Accordingly, the general object of this invention is to provide improved apparatus for measuring the extent of contaminants in a fluid.
Another object is to provide improved fluid contaminant testing apparatus which closely simulates the physical configuration of apparatus that will be encountered in use.
Another object is to provide improved fluid contaminant testing apparatus in which the extent to contaminants is determined as a function of a change in pressure.
Another object is to provide an improved fluid contaminant testing apparatus in which the extent of contaminants is determined as a function of position.
Still another object is to provide improved methods for testing the level of contaminants in a fluid.
These and other objects and advantages will become apparent from the foregoing and ongoing written specification, the drawings and the appended claims.